PHP isn’t technically an object-oriented language as such, but it is a language which allows for object-orientation, rather than forcing it. PHP is more of a procedural language generally.
By learning PHP, it will be a while before you really pick up on OOP because you need to learn the basics first. However, that’s probably a good thing - if you start with a language such as C# or Java, you have to learn the language and OOP at the same time, which can lead to confusion and a steeper learning curve.
I suppose the beauty of PHP is that whilst a pro can create an application which is efficient and adaptable/plugin-able (most likely in OOP but I have seen it done procedurally), a beginner can create an application which does the same thing - without the efficiency and plugin-ability, but it works.
The main difference is, with OOP (if you know what you’re doing) you can cut down the amount of code required. For example, an application with 10,000 lines in procedural-style coding can be converted into an application with 2,500 lines using OOP.
At first, however, most programmers can’t improve application efficiency using OOP, until they have learned OOP methodology. It’s one thing to use objects to assist your application - its another thing to use objects as the actual building blocks of your application.
Typically (not always), the first part of learning OOP is usually using an object to hold data, for example a class which replicates the structure of a database table, and can hold a row of information.
The second part is where you start to use polymorphism and composition to connect your objects and use similar objects in the same way.
The third is when you start creating a way for your whole application to run under control of specific objects.
I think the most fun with OOP is building something that has no real relevance in the real web-programming world. For example, objects representing real-life things, and pass it to a chain of objects which manipulate it in different ways. Of course, that just hammers in the OOP methodology but it teaches design patterns in a more exciting way.